The invention relates to a multistage compression type rotary compressor (hereinafter referred to as multistage rotary compressor) comprising an electric element in a hermetic shell case, and first and second rotary compression elements which are driven by the electric element, wherein a refrigerant which is compressed by the first rotary compression element and discharged is drawn into and compressed and discharged by the second rotary compression element, and a refrigeration circuit system using the multistage rotary compressor.
In a conventional multistage rotary compressor of this type, for example, in a multistage rotary compressor of an internal intermediate pressure type, for example, as disclosed in JP-H 2-294586 and JP-H 2-294587 and a refrigeration circuit system using the multistage rotary compressor, a refrigerant is drawn into a low pressure chamber of a cylinder through a suction port of a first rotary compression element (first stage compression mechanism), and it is compressed during the operation of a roller and a vane and is changed into a refrigerant having an intermediate pressure (hereinafter referred to as intermediate pressure refrigerant) and the intermediate pressure refrigerant is discharged from a high pressure chamber of the cylinder to a hermetic shell case through a discharge port and a noise eliminating chamber.
The intermediate pressure refrigerant in the hermetic shell case is drawn into the low pressure chamber of the cylinder through a suction port of a second rotary compression element (second stage compression mechanism), where it is subjected to a second stage compressions during the operation of the roller and vane and is changed into a refrigerant having a high temperature and high pressure (hereinafter referred to as high temperature and high pressure refrigerant), which in turn flows from the high pressure chamber into a radiator or the like such as an external gas cooler or the like constituting a refrigeration circuit system unit through a discharge port and the noise eliminating chamber, where the heat is radiated to perform heating operation, then throttled by an expansion valve (pressure reducing device) and enters an evaporator, where heat of the refrigerant is withdrawn and the refrigerant is evaporated, thereafter it is drawn into the first rotary compression element. This cycle is repeated.
In such a multistage rotary compressor, the cylinders of the first and second rotary compression elements and the noise eliminating chamber communicate with each other by the discharge port. A discharge valve for freely opening and closing the discharge port is provided in the noise eliminating chamber. The discharge valve is formed of an elastic member made of longitudinal substantially rectangular metal sheet wherein one side of the discharge valve is brought into contact with the discharge port to seal it and the other side of the discharge valve is fixed to an attachment port by a caulking pin with a predetermined distance relative to the discharge port.
The refrigerant which is compressed by the cylinder to reach a predetermined pressure pushes the discharge valve which closes the discharge port to open the discharge port and then it is discharged into the noise eliminating chamber. When the discharge of the refrigerant approaches an end time, the discharge vale is structured to block off the discharge port. At this time, the refrigerant remains in the discharge port which is returned to the cylinder and is expanded again.
Although the re-expansion of the refrigerant remaining in the discharge port incurs the lowering of the compression efficiency, the conventional multistage rotary compressor sets the ratio of S2 to S1 (S2/S1) to be the same as the ratio of V2 to V1 (V2/V1) where SI is an area of a discharge port of the first rotary compression element and S2 is an area of a discharge port of the second rotary compression element, V1 is displacement of the first rotary compression element and V2 is displacement of the second rotary compression element.
Meanwhile, in a refrigeration circuit system such as a cooling, heating and hot water supply unit using refrigerant, e.g., Carbon dioxide (CO2), which is large in difference between high and low pressures, a discharge pressure of the second rotary compression element (second stage) is normally controlled to a very high pressure ranging from 10 MPa to 13 MPa so that volume flow at the discharge port of the second compression element is very small. Accordingly, even if the area of the discharge port of the second rotary compression element is made small, it is hardly susceptible to a passage resistance. Nonetheless, if the ratio of S2/S1 of the discharge port is set to a conventional ratio in the multistage rotary compressor using such a refrigerant, there arises a problem that a compression efficiency (operation efficiency) is lowered.
In the multistage rotary compressor using such a refrigerant, a discharge refrigerant pressure reaches 1 MPa at a refrigerant discharge side of the second rotary compression element (second stage compression mechanism) which becomes a high pressure at an ambient temperature of about +20xc2x0 C. as shown in FIG. 5, while it reaches 9 MPa at the first rotary compression element forming a lower stage, which in turn becomes an intermediate pressure in the hermetic shell case (pressure in a case). A pressure (low pressure) drawn by the first rotary compression element is about 5 MPa.
However, if an evaporation temperature of the refrigerant increases when an ambient temperature increases, a pressure drawn by the first rotary compression element increases so that a pressure at the refrigerant discharge side (first stage discharging pressure) also increases as shown in FIG. 5. When the ambient temperature becomes not less than +32xc2x0 C., the pressure at the refrigerant discharge side (intermediate pressure) of the first rotary compression element becomes higher than that (second stage discharging pressure) of the second rotary compression element so that there occurs an inverse of the pressure between the intermediate pressure and a high pressure, arising a problem that a vane of the second rotary compression element is prone to jump to generate noises and the operation of the second rotary compression element becomes unstable.
Although in the conventional multistage rotary compressor, a pressure reversing phenomenon, between the pressure (intermediate pressure) at the refrigerant drawing side of the second rotary compression element and the pressure (high pressure) at the refrigerant discharge side of the first rotary compression element caused by excessive compression by the first rotary compression element is avoided by controlling the amount of circulation of the refrigerant by the expansion valve in the refrigeration circuit, namely, by restraining (throttling) the amount of refrigerant which is introduced into the first rotary compression element. However, in such a case, there arises a problem that the performance of the multistage rotary compressor is lowered because the amount of refrigerant which circulates in the refrigeration circuit is reduced. In addition, the pressure in the hermetic shell case increases, arising a problem that the pressure exceeds an allowable limit of the hermetic shell case.
The invention has been developed to solve the technical problems of the conventional multistage rotary compressor. It is a first object of the invention to provide a multistage rotary compressor using a refrigerant such as carbon dioxide (CO2) which becomes high in a discharge pressure, and improving operating efficiency by appropriately setting the ratio between the air volumes of the respective rotary compression elements and the areas of discharge port thereof. It is another object of the invention to provide a multistage rotary compressor capable of avoiding a pressure reversing phenomenon where discharge pressures of the first and second rotary compression elements are reversed by an ambient temperature, and a refrigeration circuit system using the multistage rotary compressor.
That is, since the multistage rotary compressor of the first aspect of the invention comprises an electric element in a hermetic shell case, and first and second rotary compression elements being driven by the electric element, wherein a refrigerant which is compressed and discharged by the first rotary compression element is drawn into and compressed by the second rotary compression element and discharged thereby, and the multistage rotary compressor is characterized in that ratio of S2/S1 is set to be smaller than ratio of V2/V1, where S1 is an area of a discharge port of the first rotary compression element, S2 is an area of a discharge port of the second rotary compression element, V1 is displacement of the first rotary compression element, and V2 is displacement of the second rotary compression element, it is possible to reduce the amount of a high pressure gas remaining in the discharge port of the second rotary compression element by further reducing the area S2 of the discharge port of the second rotary compression element.
Particularly, in the second aspect of the invention, if the ratio of S2/S1 is set to be not less than 0.55 to not more than 0.85 times as large as the ratio of V2/V1, an operating efficiency of the rotary compressor can be further enhanced.
Further, in the third aspect of the invention, if the ratio of S2/S1 is set to be not less than 0.55 to not more than 0.67 times as large as the ratio of V2/V1, the multistage rotary compressor achieves the effect particularly under circumstances such as at a cold district or the like where the flow rate of a refrigerant is small.
Still further, in the fourth aspect of the invention, if the ratio of S2/S1 is set to be not less than 0.69 to not more than 0.85 times as large as the ratio of V2/V1, the multistage rotary compressor has a dramatic effect under circumstances such as at a warm district or the like where the flow rate of a refrigerant is large.
According to the fifth aspect of the invention, since the refrigeration circuit system comprises an electric element in a hermetic shell case enclosure, and first and second rotary compression elements being driven by the electric element, wherein an intermediate pressure refrigerant which is compressed by the first rotary compression element is drawn and compressed by the second rotary compression element and discharged thereby, and the multistage rotary compressor comprises a communication path for communicating between a path through which the intermediate pressure refrigerant compressed by the first rotary compression element flows and a refrigerant discharge side of the second rotary compression element, and a valve unit for opening and closing the communication path, wherein the valve unit opens the communication path when a pressure of the intermediate pressure refrigerant becomes higher than a pressure at the refrigerant discharge side of the second compression element, it is possible to control the intermediate pressure to be not more than the pressure at the refrigerant discharge side of the second rotary compression element by the valve unit.
As a result, it is possible to avoid in advance an inconvenience of the reverse of pressures at the refrigerant suction side and the refrigerant discharge side of the second rotary compression element, and also avoid an unstable operating condition or the generation of noises, and not reduce the amount of circulation of the refrigerant, thereby avoiding the lowering of performance of the multistage rotary compressor.
In the sixth aspect of the invention, since the multistage rotary compressor further comprises a cylinder constituting the second rotary compression element, a noise eliminating chamber for discharging the refrigerant compressed in the cylinder, wherein the intermediate pressure refrigerant which is compressed by the first rotary compression element is discharged into the hermetic shell case, and the second rotary compression element draws the intermediate pressure refrigerant in the hermetic shell case thereinto, and wherein the communication path is formed in a wall forming the noise eliminating chamber for allowing the hermetic shell case enclosure to communicate with the noise eliminating chamber, and the valve unit is provided in the noise eliminating chambers or the communication path, the communication path which communicates between the path through which the intermediate pressure refrigerant compressed by the first rotary compression element flows and the refrigerant discharge side of the second rotary compression element, and the valve unit for opening and closing the communication path can be concentrated at the noise eliminating chamber of the second rotary compression element, so that the entire structure of the multistage rotary compressor can be simplified and the entire dimensions thereof can be made small.
In the seventh aspect of the invention, since the refrigeration circuit system comprises a multistage rotary compressor formed of an electric element in a hermetic shell case, and first and second rotary compression elements being driven by the electric element, wherein a refrigerant which is compressed by the first rotary compression element is compressed by the second rotary compression element, a gas cooler into which the refrigerant discharged from the second rotary compression element flows, a pressure reducing device connected to an outlet side of the gas cooler, and an evaporator connected to an outlet side of the pressure reducing device, wherein the refrigerant discharged from the evaporator is compressed by the first rotary compression element, the refrigeration circuit system further comprises a bypath circuit for supplying the refrigerant discharged from the first rotary compression element to the evaporator, a flow regulating valve capable of controlling flow rate of the refrigerant flowing in the bypath circuit, and control means for controlling the flow regulating valve and the pressure reducing device, wherein the control means normally closes the flow regulating valve and increases flow rate of the refrigerant flowing in the bypath circuit by the flow regulating valve in response to the increase of pressure at the refrigerant discharge side of the first rotary compression element, the refrigerant discharged from the first rotary compression element can be let out toward the evaporator via the bypath circuit by the flow regulating valve when the pressure at the refrigerant discharge side of the first rotary compression element increases. As a result, it is possible to avoid in advance an inconvenience of the reverse of the pressure at the refrigerant discharge side of the first rotary compression element, which increases abnormally, e.g., owing to high ambient temperature, to the pressure at the refrigerant discharge side of the second rotary compressor element are reversed.
In the eighth aspect of the invention, since the refrigerant compressed by the first rotary compressor element is discharged into the hermetic shell case and the second rotary compression element draws the refrigerant in the hermetic shell case thereinto; and wherein the control means opens the flow regulating valve when a pressure in the hermetic shell case reaches a predetermined pressure, it is possible to avoid in advance the drawback that the pressure in the hermetic shell case exceeds the allowable limit of the pressure in the hermetic shell case when the pressure at the refrigerant discharge side of the first rotary compression element increases provided that the flow regulating valve opens when the pressure in the hermetic shell case, for example, approaches the allowable pressure in the hermetic shell case.
Further, in the ninth aspect of the invention, since the control means opens the flow regulating valve when the pressure at the refrigerant discharge side of the first rotary compression element is higher than or approaches a pressure at the refrigerant discharge side of the second rotary compression element, it is possible to avoid the pressure reversing phenomenon between the pressure at the refrigerant discharge side of the first rotary compression element and that of the second rotary compression element, thereby avoiding in advance an inconvenience that the second rotary compression element falls into an unstable operating condition.
Further, in the tenth aspect of the invention, since the control means fully opens both the pressure reducing device and the flow regulating valve when the evaporator performs defrosting operation, it is possible to eliminate frost generated in the evaporator by the refrigerant compressed by the first rotary compression element and the refrigerant compressed by the second rotary compression element and also possible to avoid the pressure reversing phenomenon between the pressure at the refrigerant discharge side of the first rotary compression element and that of the second rotary compression element while more efficiently defrosting the frost grown up in the evaporator.